What does urban exploration mean:

Urban exploration (often shortened as urbex or UE) is the examination of the normally unseen or off-limits parts of urban areas.
Ventures into abandoned structures are perhaps the most common example of urban exploration.
At times, sites are entered first by locals, and may sport large amounts of graffiti and other acts of vandalism.
Urban exploration is a hobby that comes with a number of inherent dangers.So if you are going to enjoy urban exploration
always thinking about your own safety and that of another. And treat urban exploration with respect. And remember never vandalize, steal or damage anything.